Natural killer cell activity during treatment with fibroblast interferon

Short- and long-term effects on natural cytotoxicity (NC) of i.v. administration of human fibroblast interferon (IFN--beta) was studied in patients with HBsAg positive chronic active hepatitis. Short-term kinetics demonstrated after a transient fall of NC a severalfold increase of NK activity after 24 hours. Long-term kinetics of NC revealed following features: The highest relative increase was seen during the initial phase of IFN--beta application. In all patients monitored so far the enhanced NK activity could be maintained during 2 to 4 weeks of therapy. Over a period of several weeks a gradual decrease of augmented NK activity was observed in spite of continued application of high doses of IFN--beta. These findings indicate that in-vivo administration of IFN--beta results in an augmentation of natural cytotoxicity in man. Prolonged treatment with IFN--beta seems to "exhaust" the NK cell system.